This invention relates to a process for the vapor phase, catalytic addition of gaseous hydrogen cyanide to alkyl carboxylate esters having an olefinic carbon to carbon double bond.
There are several known methods for hydrocyanating unactivated olefins in the vapor phase. Teter, U.S. Pat. No. 2,385,741 describes the addition of hydrogen cyanide to unactivated olefins in the presence of a finely divided metallic cobalt catalyst. Davis, U.S. Pat. Nos. 3,278,575 and 3,278,576, discloses that finely divided metallic nickel or palladium can also be employed to catalyze the addition of hydrogen cyanide to unactivated olefins. The highest yield of organic nitriles obtained by any of these processes is 42%.
Houben-Weyl, Bond VIII, Methoden Der Organischem Chemie Sauerstoffverbindgungen III, 1952 at pages 266-278 describes the hydrocyanation of various olefinic compounds. Most of the reactions described are liquid phase reactions, some using alkaline catalysts such as KCN. A vapor phase reaction disclosed in Houben-Weyl utilizes an aluminum or silicon dioxide catalyst, preferably activated with a heavy metal salt such as cupric cyanide or zinc cyanide.
Coraor, U.S. Pat. No. 2,904,581 discloses that organic nitriles can be prepared from activated olefins. Activated olefins are hydrocarbons which contain an activating group in close proximity to an olefinic carbon atom. Preferably this activating group is adjacent to an olefinic carbon. Yields as high as 80% have been obtained by this process. Unfortunately, this is a liquid phase process and both hydrogen cyanide and the activated olefin tend to polymerize at the disclosed reaction conditions. Also, it is very difficult to separate the homogeneous catalyst from the reaction product.